Egyptian Journal of Aquatic Biology & Fisheries Zoology Department, Faculty of Science, Ain Shams University, , . ISSN 1110 - 6131 Vol. 22(3): 99- 110 (2018) ejabf.journals.ekb.eg

Association pattern among different snails and other macroinvertebrate at certain freshwater courses in Egypt

Kadria M. A. Mahmoud and Sara S. M. Sayed Department of Environmental Research and Medical Malacology, Theodor Bilharz Research Institute, .

ARTICLE INFO ABSTRACT Article History: The objective of the present work is to study the association among Received: June 2, 2018 snail species, as well as between gastropods and other macroinvertebrates. Accepted: July 5, 2018 The study was accomplished in three governorates; Giza, and Available online:July8,2018 Minya from spring (2009) till winter (2010). A total of 26 ______macroinvertebrates taxa representing 14 orders were recorded at 18 investigation sites, included Ephemeroptra, Plecoptera, Trichoptera, Keywords: Diptera, Cleoptera, Odonata, Hemiptra, , Bivalva, Decapoda, Macroinvertebrates Amphipoda, Oligochaeta, Arachnids and Hirudinea. The present data, Gastropoda revealed that the snails were the most dominant, comparing to other Association macroinvertebrates taxa in all stations of the study, which recorded Diversity Index 34.56% followed by shrimps (28.34%). Lanistes carinatus, Evenness Index bulimoides and Physa acuta were the most dominant snail species during Egypt the whole study. According to Diversity Index (H′) rank, the status of the present investigated sites ranged from poor to bad status. Moreover, Evenness Index (J) indicated that individuals at S5 (1.0), S4 and S17 (0.9) were distributed equally, while individuals at S3 (0.3), S10 (0.4) and S18 (0.41) were not. Biomphalaria alexandrina was the only species which maximally associated with leeches and this indicates its higher tolerance than other snails. All sensitive taxa (Ephemeroptra, Plecoptera and Trichoptera) were negatively correlated with Hirudinea. Meanwhile, Gastropoda was negatively correlated with Cleoptera, Hemiptra and Hirudinea. Lymnaea natalensis and Bulinus truncatus snails were found highly associated with damselflies and dragonflies, which reflect the sensitivity of these snails. Cluster analysis showed a similarity level between macroinvertebrates orders. This study concluded that most snail species were associated with moderately to somewhat pollutant tolerant macroinvertebrates, which reveals that the strength of this group in different mechanisms to tolerate pollution and other stresses.

INTRODUCTION

There are a huge number of invertebrates; worms, insects, snails and crustaceans live in water, providing food for other and serving as part of a very important aquatic food (Covichet al., 1994; Garcia et al., 2006; Andrew and Michael, 2007). Recently several Investigators used freshwater macroinvertebrates for biological assessments of water quality (Sandin and Hering, 2004; Ducrot et al., 2005; Buss and Borges, 2008).

100 Kadria M. A. Mahmoud and Sara S. M. Sayed

Macroinvertebrates are considered an important component in the ecological dynamics of lotic environments that they play significant roles in energy fluxes and nutrient cycles (Choubisa and Sheikh, 2013; Blagojević et al., 2014). In addition, gastropods are common and conspicuous elements of the freshwater macroinvertebrates taxon. Also, they serve as sensitive bioindicator-organisms of aquatic ecosystem pollution (Jagtap et al., 2011; Ali et al., 2012; Hookham et al., 2014; Lewin, 2014). Freshwater molluscs are known to play significant role in public and veterinary health (Husein et al., 2011; Saddozai et al., 2013). Some species of snails have a medical important role in transmission of some endemic diseases. In Egypt, schistosomiasis is transmitted to human by snail intermediate hosts Bulinus truncatus for Schistosoma haematobium and Biomphalaria alexandrina for Schistosoma mansoni, which are prevalent in both Upper and Lower Egypt (El-Emam et al., 1996; WHO, 2012) and Lymnaea natalensis intermediate host for fascioliasis (Kaplan, 2001). Predation, competition and commensalism relationships occurred between all communities that live in the same habitat. Competitive interaction between snails and other macroinvertebrate algaivores is strong. In addition to the physical competition for food and other resources one would ordinarily expect as density increases and beyond the general degradation of the environment by waste products and oxygen depletion (Dillon, 2000). Freitas and Santos (1995) and Giovanelli et al. (2005) studied the snail-snail interactions, with special emphasis on competition, stated that Melanoides tuberculatus is capable to reach high densities; hence, competition for space is also possible. However, the outcome of the interactions between M. tuberculatus and Biomphalaria spp. seems to be related to the habitat type where both species occur in Kenya (Mkoji et al., 1992). The multiple-predator approach not only reflects nature well, but also provides a richer ecological framework where by adaptive trade-off between predators ultimately can be connected to other aspects of ecology, particularly to higher order community effects (Karieva, 1994). Generally, molluscs may face many predators of other macroinvertebrates at least four functional classes, such as carnivorous leeches, certain crustaceans (crab, crayfishes and ostracods), aquatic Cleoptera, dystiscid beetles and fish (Cibrowski and Corkum, 2003). The leech Glossiphonia complanata does not appear to have substantial impact on snail populations, but this may be due to most studies focusing on adult snails rather than juvenile snails. Thus, there was a comparatively large effect of leech predation on newly-hatched snails, due to a high probability of encounter and high predation rates (Brönmark, 1992). Crayfish primarily attack snails via the aperture (Alexander and Covich, 1991; Stephanie et al., 2001). In addition, anecdotal information suggests that relatively large crayfish may sometimes also use shell-crushing or spire-snapping attacks (Vermeij and Covich, 1978). Predators attack Physa primarily through shell entry (by crayfish, Orconectes obscurus) and shell crushing (by fish, Lepomis gibbosus, Cyprinus carpio, Carrasiu sauratus). The narrow apertures associated with elongate shells were expected to restrict apertures access by crayfish (DeWitt et al., 2000). The present study aims to investigate the association in-between snail species in some freshwater courses of Egypt and the association between snails and other species of macro-invertebrates predators or competitors.

Association pattern among different snail species and other macroinvertebrates 101

MATERIALS AND METHODS

Study area: Samples were collected from 18 sites in Giza, Damietta and Minya governorates from spring (2009) till winter (2010). The watercourses included River , branches and drains as follows: sites from (S1: El-Ayyat; S2: El-Saff; S3: El- Warrak- ;S4: El-Koratten; S5: El-Kanater, S6: Gezert El-Sayala and S7: El-Hooddrainage), (S8: Bostan; S9: Adlyia; S10: Damietta; S11: El-kashf and S12: El- Sarw drainage) and (S13:Menia, S14: Samaloot; S15: Matay; S16: BaniMazar, S17: and S18: El- Moheet drainage) (Fig. 1).

Fig. 1: A map of Egypt showing Minya, Giza and Damietta governorates.

Field samples: From each site macro-invertebrates, including freshwater snails were collected by 500 μm-mesh D-Form dip net with a fixed number of five filled net strikes. The five samples were then pooled, representing a single sample for each site (Noumi, 2008). In the laboratory, samples were washed in a 500 μm-mesh sieve to remove sand and macro-invertebrates were sorted and all taxa were separated; enumerated and identified under a binocular dissecting microscope. Macro-invertebrates were identified to the latest taxonomical level (Leska, 1998; Bouchard, 2004). While snails sorted, counted and identified according to Ibrahim et al. (1999). Statistical analysis: :was used according to Shannon-Wiener (1949) formula (׳Diversity Index (H H′= -∑ [ni/N] ln [ni/N] Where ni is the number of individuals in each species, N equals the total number of individuals in the sample,ln = natural logarithm and ∑ equals the total number of species in the sample. Results are generally between >4 = high status, 3- 4= good status, 1- 2= poor status and <1 =bad status. Evenness Index (J) was used according to Pielou (1966) formula: J = H′/ In S H′= Shannon– Wiener diversity index, ln = natural logarithm and S = total number of species in the sample. The values are between 0– 1.When the value is getting closer to 1, it means that the individuals are distributed equally. 102 Kadria M. A. Mahmoud and Sara S. M. Sayed

Cluster analysis and correlation coefficients between macro-invertebrates’ orders were performed. Data for each snails’ site group were analyzed linear by linear association analysis and Chi square test. The data were considered significant if P- value was ≤0.05, highly significant if P<0.01 and very highly significant if p<0.001. All statistical analysis was performed using SPSS computer program (version 18 windows).

RESULTS

Distribution and density of macroinvertebrates community in the study sites: Results of the distribution and density of collected macroinvertebrates are summarized in Table (1). A total of 26 macroinvertebrates taxa representing 14 orders were recorded from 18 investigation sites, during the study period; included Ephemeroptra, Plecoptera, Trichoptera, Diptera, Cleoptera, Odonata, Hemiptra, Gastropoda, Bivalva, Decapoda, Amphipoda, Oligochaeta, Arachnids and Hirudinea. Generally, the most dominant macroinvertebrates taxa were aquatic snails and shrimps, which recorded 561 and 460, respectively. 13 species of gastropods and one bivalve belonging to class Pelecypoda, family Corbiculidae were identified from the investigated sites during two successive years. Snail species were, Biomphalaria alexandrina, Bulinus truncatus, Lymnaea natalensis, Lanistes carinatus, Cleopatra bulimoides, Helisoma duryi, Bellamya unicolor, Planorbis planorbis, Physa acuta, Melanoides tuberculata, Theodoxus niloticus, Valvata nilotica, Succinea cleopatra and the bivalve species Corbicula consobrina. Data in Fig. (2) shows the total number of different snail species collected during the study. The most abundant species were L. carinatus(109 specimens), C. bulimoides (102 specimens) and P. acuta (96 specimens).

Fig. 2: Total number of collected snails' species during the study period.

According to Diversity Index (H′) rank the status of the present investigated sites ranged from poor to bad status. While the highest H′ index value was recorded (2.25) at S5, the lowest value was (0.456) at S18. However, Evenness Index (J) indicated that individuals at S4 (0.9), S5 (1.0), S9 (0.8) and S17 (0.9) were distributed equally, while individuals at S3 (0.3), S10 (0.4) and S18 (0.41) were not (Fig. 3). Association pattern among different snail species and other macroinvertebrates 103

Table 1: Distribution and density of macroinvertebrates at studied sites.

Macroinvertebrates Giza sites Damietta sites Minya sites To tal/ Order Taxa S S S S S S S S S S S S S S S S S S tax 1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 a 0 1 2 3 4 5 6 7 8 Epheme Mayfly 0 0 3 1 1 1 0 1 3 0 0 0 1 0 1 0 1 0 60 roptra 1 9 0 1 Plecopt Stonefly 0 0 4 1 3 3 0 3 0 0 2 2 0 0 0 0 0 0 18 era Trichop Caddisfly 0 0 0 0 0 0 0 2 0 0 0 0 3 0 0 0 3 0 8 tera Diptera Midge 1 0 0 3 4 7 0 0 0 0 0 0 0 0 0 0 1 1 17 Cleopte Riffle 0 0 0 0 1 0 0 0 0 4 0 0 1 1 2 0 0 0 9 ra beetle Water 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 penny Whirligig 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 beetle Crawling 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Diving 0 1 0 0 2 0 4 0 0 0 0 0 0 0 0 1 3 0 11 dytiscidae Odonat Damselfly 2 2 6 1 1 8 0 6 1 1 3 4 2 1 1 4 8 0 96 a 8 8 2 Dragonfly 3 2 1 1 8 3 1 1 7 0 2 2 1 1 2 1 8 0 90 7 3 Hemipt Water 0 0 0 2 0 3 7 0 0 0 0 2 0 3 0 0 2 1 20 ra strider True bugs 3 0 0 1 5 0 1 1 6 2 1 1 0 9 0 6 0 1 79 5 1 9 Water 0 1 0 0 0 0 0 1 9 0 0 0 0 0 1 0 0 1 13 scorpion Water 0 0 0 2 2 0 5 1 2 0 1 3 1 0 0 2 0 0 19 boatman Backswim 0 0 0 0 0 0 3 0 0 0 0 1 0 0 0 0 5 0 9 mer Gastrop Aquatic 6 4 8 4 3 5 3 5 3 3 2 5 4 6 2 1 2 0 56 oda Snails 0 0 9 4 2 1 7 4 0 1 5 7 5 1 Bivalva Bivalves 0 0 2 1 1 3 0 0 0 0 4 0 0 1 0 0 1 0 93 5 8 9 4 Decapo Shrimps 5 1 2 7 5 8 0 3 5 0 7 0 1 6 1 3 1 0 46 da 2 4 7 1 1 6 2 5 1 2 5 0 Crayfish 0 0 0 1 0 0 0 1 0 0 1 0 2 1 3 0 0 0 9 Amphip Scuds 0 0 0 0 0 0 0 0 0 9 0 1 0 0 0 0 0 0 10 oda Oligoch Aquatic 6 0 0 2 0 1 0 0 0 0 0 0 0 0 2 0 0 0 30 aeta worms 1 Arachni Fishing 0 0 0 1 0 0 1 0 0 0 1 0 0 0 0 0 0 0 3 ds spider Hirudin Leeches 2 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 4 ea Rat-tailed 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0 1 4 maggots Total / site 8 5 1 1 1 2 7 1 1 1 2 3 6 1 4 6 9 2 16 2 8 0 9 6 4 3 0 2 9 4 1 4 0 8 3 5 3 23 8 5 9 0 2 6 3 Total/ governorate 925 302 396

104 Kadria M. A. Mahmoud and Sara S. M. Sayed

Fig. 3: Diversity Index (H′) and Evenness Index (J) for studied sites.

Association between snails and other macroinvertebrates: Results of association pattern between different snail’s species and 15 different macroinvertebrates throughout the study period are represented in Table (2). No association was detected between B. alexandrina and each of mayflies, caddisflies and water strider and the least association percentage with each of midge flies and riffle beetle whereas the maximum association was detected with true bugs (38%) and leeches (13%) which are somewhat pollutant tolerant, respectively consequently this snail species has the same ability of tolerance and so their association attributed to habitat preference. B. truncatus was found associated with all different macroinvertebrates, and the maximum association was detected with each of damselflies (21%) and dragonflies (19%) and all of them are predators. L. natalensis was found in association with all different macroinvertebrates, and the maximum association was detected with each of riffle beetle (27%), damselflies (27%), dragonflies (25%) then true bugs (23%) and so the association pattern approximately like B. truncatus. Also, T. niloticus shared the approximately same pattern with these snail species but with exception that no association with leeches was recorded. In addition, H. duryi snails shared with them the same pattern but they maximally associated with crayfish. B. unicolor approximately equally associated with most macroinvertebrates and was recorded no association with water penny and backswimmer. M. tuberculatawas found in association with most macroinvertebrates while the maximum association was detected with each of damselflies, dragonflies, true bugs, water boatman and crayfish which are predator except water boatman which is omnivorous. M. tuberculata did not associate with water penny and leeches). P. planorbishas limited distribution associated only with damselflies while maximally associated with crayfish followed by dragonflies and stoneflies then each of mayflies, damselflies and true bugs and at last with riffle beetle. So, each of caddisflies, midgeflies, water penny, water strider, true bugs, water scorpion, water boatman, backswimmer and leeches were not recorded in association with P. planorbis. It maximally associated with stoneflies then each of caddisflies, damselflies, dragonflies and crayfish whereas did not associate with the rest of macroinvertebrates. As with P. planorbis,C. consobrina was found in association with all macroinvertebrates except water penny, and the maximum association was detected with each of stoneflies, damselflies, dragonflies, mayflies, true bugs and crayfish. B. alexandrina was the only species which maximally associated with leeches. Association pattern among different snail species and other macroinvertebrates 105

Table 2: Association pattern between macroinvertebrates and different snail species during the study period. Macroinvertebrates Snails Order Taxa B.a B.t L.n L.c B.u C.b P.a H.d V.n P.p M.t T.n S.c C.c Ephemeroptra Mayflies 0 11 9 8 10 8 8 14 0 6 7 11 7 11 Plecoptera Stoneflies 8 6 5 6 9 8 8 5 7 13 3 5 9 8 Trichoptera Caddisfly 0 1 1 2 5 2 2 3 3 0 1 2 1 2 Diptera Midge 3 5 5 4 2 4 5 5 0 0 7 5 6 7 Riffle Beetle 3 8 8 8 6 7 7 14 0 2 9 9 5 6 Cleoptera Water Peny 7 1 0 1 0 1 2 1 0 0 0 1 2 1 Dameslfly 16 21 19 19 22 20 19 18 3 25 24 24 20 19 Odonata Dragon fly 17 19 17 16 20 15 16 19 3 19 20 17 14 15 Water strider 0 5 3 5 4 7 6 4 0 0 6 4 2 3 True Bugs 38 12 17 16 12 15 17 20 0 6 20 14 19 15 Water 8 9 6 5 5 4 5 4 0 0 7 3 7 4 Hemiptra Scorpion Water 6 8 7 7 10 6 6 8 0 0 9 7 5 7 Boatman Backswimmer 3 1 1 2 0 2 1 0 0 0 2 1 1 0 Decapoda Cray fish 5 11 9 11 11 13 12 14 3 25 27 8 13 11 Hirudinea Leeches 13 0 2 2 1 1 2 1 0 0 0 0 0 1

Correlation between macroinvertebrates orders: Mostly, macroinvertebrates orders were correlated whether positively or negatively as shown in Table (3). All sensitive taxa (Ephemeroptra, Plecoptera and Trichoptera) were negatively correlated with Hirudinea. Meanwhile, Gastropoda was negatively correlated with Cleoptera, Hemiptra and Hirudinea.

Table 3: Correlation among macroinvertebrates orders. Ephem- Plecop- Tricho- Cleop- Odon- Hemip- Gastrop- Decap- Hirud- Order Diptera eroptra tera ptera tera ata tra oda oda inea - Ephemeroptra 0.636** 0.715** 0.570** 0.198 0.137 0.526** 0.390** - Plecoptera 1 0.502** 0.323* 0.527** -0.229 0.423** 0.034 -0.273* 0.343** - - Trichoptera 1 1 0.536** -0.334* 0.093 -0.081 0.339** 0.379** - Diptera 1 0.129 0.977** -0.088 0.314* 0.778** 0.398** Cleoptera 1 0.096 0.443** -0.271* 0.015 -0.087 Odonata 1 -0.054 0.301* 0.780** -0.220 Hemiptra 1 -0.596** 0.175 0.346** Gastropoda 1 0.156 -0.155 Decapoda 1 -0.045 Hirudinea 1 *refer to significant correlation at P<0.05 and ** refer to highly significantcorrelation at P<0.01.

On the other hand, there were a highly significant positive correlation (P<0.01) between Diptera and Odonata (0.977) and Plecoptra and Gastropoda (0.423) and that confirmed by cluster analysis (Fig. 4), which showed a similarity level between the mentioned macroinvertebrates orders.

106 Kadria M. A. Mahmoud and Sara S. M. Sayed

Fig. 4: Cluster analysis showed the similarity level between macroinvertebrates groups depending on correlation coefficient distance.

Freshwater molluscs play an important role in aquatic ecosystems, providing food for many fish species (McMahon and Bogan, 2001; Garcia et al., 2006; Fagundes et al., 2008) and vertebrates (Cummins and Bogan, 2006). The fresh water molluscs were identified in the study sites (El-Minya, Giza and Damietta governorates, Egypt) as B. alexandrina, B. truncatus, L. natalensis, L.carinatus, C. bulimoides, H. duryi, B. unicolor, P. planorbis, P.acuta, M.tuberculata, T. nniloticus, V. nilotica, S. cleopatra and the bivalve species C. consobrina. This agrees with the observation reported by Ibrahim et al. (2004) who mentioned that the community of freshwater snails in Al-Salam canal comprised 11 species, namely: L. carinatus, B. unicolor, M. tuberculta, C. bulimoides, Cleopatra cyclostomoides, Theodoxus niloticus, H. duryi, B. alexandrina, B. truncatus, P. acuta and L. natalensis. Recently, Marie et al. (2015) demonstrated that 12 snail species namely; B. alexandrina, P. acuta, L. natalensis, B. truncatus, S. cleopatra, B. unicolor, M. tuberculata, H. duryi, L. carinatus, C. bulimoides, P. planorbis and Biomphalaria glabrata were recorded in selected sites from four Egyptian governorates (Giza, Ismailia, Menoufia and Gharbia). This gives an indication of stable coexistence found in the same habitat, which are capable of supporting mutually exclusive and conductive niches for different species population. The current study explored that the snails intermediate host of schistosomiasis, B. alexandrina and B. truncates were mostly found associated with L. natalensis, P. acuta followed by C. bulimoides, L. carinatus and C. consobrinathen S. cleopatra. This coincides with Yousif et al. (1998) stated that both vector snails of schistosomiasis in his study areas were in many cases associated with several other snail spp such as the pulmonate Planorbis planorbis, P. acuta and L. natalensis and the prosobranchs M. tuberculata, L. carinatus, C. bulimoides, B. unicolor and T. niloticus. On the other hand, the present study in contrary with Giovanelli et al. (2005) who demonstrated that no association was observed between Melanoides tuberculatus, and Physa marmorata or Biomphalaria tenagophila although all three species were most frequently encountered on the same type of habitat. In addition, in Nigeria, Ndifon and Ukoli (1989) observed that M. tuberculatus was positively associated with Physa waterloti and Biomphala riapfeifferi .The occurrence of competitive interaction between M. tuberculatus and Biomphalaria spp. only in some specific environments is related to the different life Association pattern among different snail species and other macroinvertebrates 107 strategies adopted by those species. As opposed to Biomphalaria spp., M. tuberculatus has low reproduction rates, low mortality rates, and a long life span (Pointier et al., 1991). Other factors limited the efficiency of M. tuberculatus as a competitor for Biomphalaria spp. The presence of diverse microhabitats in heterogeneous environments may favor the coexistence of M. tuberculatus with B. glabrata, as it may allow both species to avoid competition (Choudhary and Ahi, 2015). The present investigation raveled that the habitat preference of B. alexandrina is different from M. tuberculatus because B. alexandrina found associated with somewhat pollutant tolerant macroinvertebrates this opposed to M. tuberculatus association with damselflies which reflects their sensitivity. This was confirmed by Giovanelliet al. (2002) who concluded that the possibility that M. tuberculatus be more sensitive to the molluscicide than Biomphalaria spp. may lead to a reduction of the competitive interaction between those species, thus indirectly stimulating the increase in the population of Biomphalaria spp. On the other hand, some environmental modifications may add to the instability of the environment, what would make room for the coexistence of M. tuberculatus and Biomphalaria spp. (Giovanelli et al., 2005). The present work revealed that a few B. alexandrina snails, the intermediate host of S. mansoni, persisted in site of H. duryi, which may be attributed to the inter- specific competition between that snail and H. duryi. Thus, many authors recommended that using H. duryi in the biological control of B. alexandrina and B. truncatus snails (Pointier and Augustin, 1999; Pointier and Jourdane, 2000; Ibrahim et al., 2004). In addition, the association pattern of rest macroinvertebrates with different snail species may reflect either the physico-chemical habitat preference or may reflect negative correlation (due to predation or competition) or positive correlation (due to join or exchange relationships). B. truncatus was found associated with all different macroinvertebrates, and the maximum association was detected with each of damselflies and dragonflies. These macroinvertebrates are moderately pollutant tolerant and shared the habitat preference with B. truncatus, so, this confirmed the sensitivity of these snails. L. natalensis the intermediate host of Fasciola hepatica was found associated with all different macroinvertebrates, and the maximum association was detected with each of riffle beetles (27%), damselflies (27%), dragonflies (25%) then true bugs (23%).This association pattern approximately looks like B. truncatus with exception that, riffle beetles were not predators and their diet consists of microorganisms and debris, such as diatoms and true bugs were pollutant tolerant. Each of L. carinatus, P. acutaand C. bulmoides shared approximately the same pattern with L. natalensis. The results showed that B. alexandrina snails, were recorded a high value of persisting in site invaded by true bugs. The voracious behavior of water bugs is well known and it is the only species that feeds on snails during the larval and adult stages are belostomatids (Smith, 1977). Under laboratory conditions, Armuade and Estevez (2006) stated that B. elongatum showed a great ability to catch and feed on Biomphalaria sp. Moreover, Hofkin et al. (1991) and Mkoji et al. (1999) observed a strong negative association between the presence of medically important pulmonate snails and the cray fish Procambarus clarkii in freshwater habitats in Kenya. This agrees with the present study that B. alexandrina snails exist with low percent in the stations occupied by the cray fish P. clarkia which may be due to its predatory behavior on the snails.

108 Kadria M. A. Mahmoud and Sara S. M. Sayed

CONCLUSION

This study concluded that most snail species were associated with predators and moderately to somewhat pollutant tolerant macroinvertebrates and reveals the strength of this group of animals, which originated from their reproduction strategy and their different mechanisms to avoid predators or struggle against pollution and other stresses. Since freshwater snails are common and conspicuous elements of the freshwater biota, an appreciation of freshwater gastropods cannot help but leads to an appreciation of freshwater ecosystems as a whole.

ACKNOWLEDGEMENT

This work was a part from project 80 M. entitled; Assessment of certain freshwater bodies’ environment in some Egyptian Governorates.

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